A block of mass $m$ rests on an inclined plane and is attached by a string to the wall as shown in the figure. The coefficient of static friction between the plane and the block is $0.25$. The string can withstand a maximum force of $20$ $N$. The maximum value of the mass $(m)$ for which the string will not break and the block will be in static equilibrium is ____________ $kg$. Take $cos\theta$ and $sin \theta$
Acceleration due to gravity $g$ = $10$ $m$/$s^2$